As semiconductor devices are getting smaller, thinner and lighter, more and more semiconductor chips are integrated in a device. The semiconductor chip is commonly mounted on a circuit board by flip-chip attach method. A typical flip-chip attach method is the controlled collapse chip connection (C4) process in which electrodes of the semiconductor chip is directly soldered with solder bumps or lands on a circuit board. After the soldering, the gap between the chip and the circuit board is sealed or encapsulated with an epoxy resin.
In conventional C4 process, the resin encapsulation is performed by capillary flow method. However, the process has drawback of low productivity due to many steps involved: 1) treatment of solder with flux, 2) soldering, 3) cleaning of the flux, 4) injection of an encapsulation resin by capillary flow method, and 5) curing of the resin. As pads are getting finer with narrower pitch, cleaning of the flux is getting more and more difficult. Residual flux on the circuit board respells an encapsulation resin, and ionic impurities in residual flux degrade reliability of a device package.
To solve these problems, U.S. Pat. No. 5,128,746 discloses a non-flow method in which soldering and resin encapsulation is performed in a single step by applying an encapsulation resin comprising flux component to a circuit board and then placing a semiconductor chip having solder electrodes on the applied resin.
For use in the non-flow method, various compositions comprising a curing agent performing as flux as well are proposed, for example, a phenolic resin as described in Japanese Patent Application Laid-Open No.2002-232123, a phenolic carboxylic acid as described in Japanese Patent Application Laid-Open No. 2003-128874, an acid anhydride as described in Japanese Patent Application Laid-Open No. 2001-329048 and 2003-160639, a carboxylic acid as described in Japanese Patent Application Laid-Open No. 2002-293883 and an aromatic carboxylic acid hydrazide as described in Japanese Patent Application Laid-Open No. 2004-303874.
A composition comprising a flux component besides a curing agent are also known. For example, a composition comprising a carboxylic acid or a block carboxylic acid as flux component in addition to a phenolic or acid anhydride curing agent are known from Japanese Patent Application Laid-Open No. 2002-190497, 2003-82064, and 2001-223227.